function start() {
  racecar = new Car;
  keys = new Keys;
}

function everyFrame() {
  if (keys.upIsPressed()) {
    racecar.accelerate();
  } else if (keys.downIsPressed()) {
    // YOUR CODE HERE
  }
  if (keys.leftIsPressed()) {
    // YOUR CODE HERE
  } else if (keys.rightIsPressed()) {
    // YOUR CODE HERE
  }
}
